1. Field of the Invention
The present invention relates to an oscillating device, making use of a torsion spring that elastically supports a member capable of vibrating torsionally, a light deflector, and an optical apparatus, such as an image forming apparatus, using the same. The light deflector is suitably used in an image forming apparatus, such as a digital copying machine or a laser beam printer using an electrophotography process, or a projection display that projects an image by light deflection and scanning.
2. Description of the Related Art
Very small mechanical members, which are manufactured from a silicon substrate by a semiconductor process, can be processed on the order of micrometers. Various very small functional elements are realized using these very small mechanical members. In particular, compared to a light-scanning optical system using, for example, a rotatable polygonal mirror, a light deflector that torsionally vibrates a reflecting surface with a micro torsion spring (formed by such a technology) can be reduced in size, and consumes little electricity.
An example of a light deflector formed of silicon is shown in FIG. 7 (refer to U.S. Pat. No. 4,317,611). FIG. 7 is a perspective view of the entire light deflector.
The light deflector shown in FIG. 7 includes a supporting portion 20, a movable portion 30, and torsion springs 22 and 24 supporting the movable portion 30 at the supporting portion 20 so that it can torsionally vibrate with respect to the supporting portion 20. The light deflector is formed by performing an etching technology and photolithography of a semiconductor producing method on a silicon wafer.
However, when an oscillating device is manufactured from a single-crystal silicon substrate by a semiconductor process such as that discussed in U.S. Pat. No. 4,317,611, variations may occur in the spring constant of the torsion springs. The variations in the spring constant cause, for example, variations in the resonant frequency of the oscillating device.